Wind farm control system and associated method

ABSTRACT

A control system and control method of a wind farm allows taking into account dynamic variations in the possibilities of reactive power generation of each wind turbine with respect to maximum reactive power generation capacities. The system is configured to receive from at least one first wind turbine of the wind turbines of the wind farm a maximum reactive power limit desired lower than a minimum reactive power capacity required. The system is configured to calculate the individual reactive power setpoints for each of the at least two wind turbines of the wind farm such that the individual reactive power setpoint for the at least one first wind turbine of the wind farm does not exceed the maximum reactive power limit desired.

CROSS-REFERENCE TO RELATED APPLICATIONS AND PRIORITY

This patent application claims priority from EP Patent Application No.18383010.8 filed Dec. 31, 2018. This patent application is hereinincorporated by reference in its entirety.

OBJECT OF THE INVENTION

The present invention relates to a control system and control method ofa wind farm which allows taking into account dynamic variations in theneeds and possibilities of reactive power generation of each windturbine with respect to maximum reactive power generation capacitiesbased on the active power they can generate at all times.

BACKGROUND OF THE INVENTION

Normally, grid integration regulations stipulate as a requirement forconnecting a wind farm to a power grid having available, under anycondition of generating active power less than or equal to the ratedpower of the wind farm, a minimum reactive power generation capacityrequired in the wind farm to offer support to the power grid in thecontrol of the voltage thereof. This in turn translates into minimumreactive power generation capacities required of the wind turbines ofthe wind farm in an individual manner, and as they are equipped withpower converters, they are converted into a suitable solution foraddressing the requirements of the grid operator, minimising the needfor connecting additional equipment in the sub-station. Said reactivepower capacity is referred to as minimum reactive power capacityrequired.

Wind turbines have maximum electric capacities sized in turn by theminimum of the maximum capacities of the components of their electricdrive (particularly generator and power converter). The maximum electriccapacities are usually specified in terms of apparent power. Saidmaximum capacities provide an indication of the maximum active power andreactive power which the wind turbines can supply during a given time.Thus, there are often different values for the maximum rated electriccapacity (i.e., that which can be sustained in a steady manner) than fortransient maximum electric capacities (those which will only besustained in a limited manner in time, for example, for less than tenminutes, one minute or several seconds). In turn, the maximum reactivepower capacity required can be lower than the maximum reactive powercapacity.

The rated apparent power S determines the rated steady active power andreactive power levels that the wind turbines can generate withoutexceeding the rated current of the electrical elements that are part ofthe electric drive (primarily generator and converter). It is usuallycalculated with a rated active power value P and a rated reactive powervalue Q according to the following expression:S=√{square root over (P ² +Q ²)}  (1)

In the state of the art, the rated reactive power and rated active powervalues determine the maximum active power and reactive power valueswhich can be sustained in a steady manner, for which purpose thosecontrol systems responsible for calculating the active and reactivepower setpoints of the wind turbines are configured so that saidsetpoints do not exceed said maximum values. That is, the controlsystems of the state of the art are configured such that the slowdynamics control loops will not calculate active power setpoints greaterthan the rated active power nor will they calculate reactive powersetpoints greater than the rated reactive power. This occurs both in thewind farm and in the wind turbine (the control systems of the wind farmand of each wind turbine are configured as previously specified).

Generally, the rated reactive power in the wind farm coincides with aminimum reactive power capacity required which must be guaranteed forcompliance with grid integration codes applicable at the point ofconnection of the wind farm to the power grid.

Reactive power is generally the control variable used for control of thevoltage of the power grid. There are different control modes forcontrolling the voltage of the power grid, where it is generally thegrid operator who specifies the most appropriate control mode in eachcase. Said operating modes coincide with different possibleimplementations in the control system of the wind farm for the controlof reactive power:

-   -   control of reactive power based on reactive power references        received directly from a remote control centre (remote control        centre which can belong to the wind farm operator or to the        power grid operator);    -   voltage control at a point of the power grid to which the wind        farm is connected which, based on the voltage measurement taken        at that point and on a voltage reference provided by the power        grid operator (either directly or indirectly through the wind        farm operator), calculates a global reactive power setpoint for        the wind farm;    -   control of the power factor at a point of the power grid to        which the wind farm is connected which, based on the active        power measurement taken at that point and on a power factor        reference provided by the power grid operator (either directly        or indirectly through the wind farm operator), calculates a        global reactive power setpoint for the wind farm;

Based on the power grid code or the control mode selected by the windfarm operator, the control system of the wind farm is configured tocalculate a total reactive power setpoint for the wind farm which islater distributed in an individual manner among the different windturbines to comply with the required setpoint. To that end, the controlsystem of the wind farm calculates individual reactive power setpointsfor the wind turbines which, when added together, amount to the totalreactive power setpoint for the wind farm.

There are solutions in the state of the art in which the control systemof the wind farm performs the distribution either equally among the windturbines of the wind farm, or it sends different setpoints for the windturbines of the wind farm taking into consideration thermal or electricloss criteria, but always without exceeding a pre-determined maximumreactive power capacity.

DESCRIPTION OF THE INVENTION

The present invention relates to a control system and control method ofa wind farm which allows calculating individual reactive power setpointsfor wind turbines, taking into account dynamic variations in the needsand possibilities of reactive power generation of each wind turbine withrespect to maximum reactive power generation capacities for the purposeof optimising the active power production. The invention also relates tothe wind farm comprising said control system of a wind farm.

In the case of a wind turbine, the rated apparent power is set in thesame way as in the state of the art. According to the invention,however, the steady active power may exceed the rated active power, forwhich the generated reactive power will be less than the rated reactivepower.

To that end, the present invention proposes a control system and acontrol method of a wind turbine configured to generate an active powergreater than the rated active power without exceeding the limit set bythe apparent power, by means of calculating a desired maximum reactivepower limit less than the rated reactive power, i.e., less than theminimum reactive power capacity required of the wind turbine.

The maximum reactive power limit desired corresponds to the reactivepower which can be generated without limitations in the active power. Itis calculated based on an initial active power or torque setpoint towhich electric limitations have not been applied and which is dependenton the operating conditions of the wind turbine (wind speed,temperature, capacity of the mechanical components) and on the ratedapparent power. Said maximum reactive power limit desired is sent to acentral wind farm control system for it to calculate a final reactivepower setpoint, which once the maximum reactive power limits desired ofeach of the wind turbines with operating conditions that allowgenerating an active power greater than the rated active power have beentaken into account, the control system will, send the final reactivepower setpoint to each of them, in the attempt to keep it as close aspossible to the available reactive power, without limitation, of each ofthem, i.e., to the respective maximum reactive power limits desired.

Once the final reactive power setpoint has been received, the controlsystem of the wind turbine will calculate a final torque or active powersetpoint for the wind turbine which, taking into account the capacity ofthe electric drive, assures that there is available reactive powercapacity to comply with the final reactive power setpoint received fromthe control system of the global reactive power setpoint in the windfarm. To that end, it will apply a maximum limit to the torque orinitial power setpoint based on the final reactive power setpointreceived from the control system of the wind farm and based on thecapacity of the electric drive.

In one embodiment, the steady reactive power can also exceed the ratedreactive power.

In a wind farm there can be wind turbines with different operatingconditions:

first wind turbines with operating conditions (wind speed and/orrotational speed, temperature of components, etc.) that give rise toinitial active power or torque setpoints resulting from the control ofthe wind turbine which cannot be taken on without compromising theminimum reactive power capacities required, and

second wind turbines with operating conditions (wind speed and/orrotational speed, temperature of components, etc.) that are such thatthe initial active power or torque setpoints resulting from the controlof the wind turbine for said operating conditions can be taken on by theelectric drive without compromising the minimum reactive powercapacities required.

This would be the case in situations in which the operating conditionsof the second wind turbines are such that they cannot generate an activepower greater than the rated active power (active power which can begenerated in a sustained manner and simultaneously with the ratedreactive power) and therefore be taken on by the electric drive withoutcompromising the minimum reactive power capacities required, whereas theoperating conditions of the first wind turbines are such that they cangenerate an active power greater than the rated active power providedthat the capacity of the electric drive is assured to that end.

For that purpose, the control system of at least one first wind turbineis configured to calculate a maximum reactive power limit desired whichis a function of the initial active power or torque setpoint and of thecapacity of the electric drive, and sending said maximum reactive powerlimit desired to the control system of the wind farm.

This allows dedicating the highest possible fraction of the set ofelectric capacities (apparent power) of the wind farm to the activepower generation such that given favorable wind conditions, the at leastone first wind turbine may exceed the rated active power level.

In order to satisfy a global reactive power setpoint of the wind farm,avoiding the necessity to limit the initial active power or torquesetpoints resulting from the control of the first wind turbines, thecontrol system of the wind farm is configured such that it can calculatethe individual reactive power setpoints taking into account for the atleast one first wind turbine at least one maximum reactive power limitdesired.

In the case of the first wind turbines, taking into account that theoperating conditions of said wind turbines are such that they may exceedthe rated active power level (that which can be provided in a sustainedmanner at the same time as the rated reactive power level), the maximumreactive power limit desired is lower than the maximum reactive powercapacity required (which is equal to the rated reactive power in oneembodiment).

The present invention refers to a control system of a wind farmcomprising at least two wind turbines, where the system is configuredto:

-   -   calculate a global reactive power setpoint for the reactive        power to be generated by the at least two wind turbines of the        wind farm at the point of connection of the farm to the power        grid;    -   calculate individual reactive power setpoints for each of the at        least two wind turbines of the wind farm such that they add up        to the global reactive power setpoint;    -   receive from at least one first wind turbine of the wind        turbines of the wind farm a maximum reactive power limit desired        lower than a minimum reactive power capacity required; and    -   calculate the individual reactive power setpoints for each of        the at least two wind turbines of the wind farm such that the        individual reactive power setpoint for the at least one first        wind turbine of the wind farm does not exceed the maximum        reactive power limit desired.

Optionally, the maximum reactive power limit desired lower than aminimum reactive power capacity required is dependent on an initialactive power setpoint of the at least one first wind turbine.

Optionally, the system is additionally configured to receive from atleast one second wind turbine of the wind turbines of the wind farm amaximum reactive power limit possible greater than a minimum reactivepower capacity required.

Preferably, the maximum reactive power limit possible greater than aminimum reactive power capacity required is dependent on an initialactive power setpoint desired of the at least one second wind turbine.

Optionally, the system is additionally configured to set a firstreactive power limit for each of the wind turbines chosen from themaximum reactive power limit desired and the minimum reactive powercapacity required, with the one chosen being the lowest in absolutevalue.

In this first embodiment, the first reactive power limit will take oneof the following possible values:

For the first wind turbine, the operating conditions are such that areactive power value less than the minimum reactive power capacityrequired by the grid operator and equal to the maximum reactive powerlimit desired can exceed the maximum active power.

For the second wind turbine, the operating conditions are such that areactive power value equal to the minimum reactive power capacityrequired by the grid operator cannot exceed the maximum active power.

Optionally, the system is additionally configured to set the firstreactive power limit for the at least one second wind turbine of each ofthe wind turbines of the wind farm equal to the maximum reactive powerlimit possible.

In this second embodiment, the first reactive power limit will take oneof the following possible values:

For the first wind turbine, the operating conditions are such that areactive power value lower than the minimum reactive power capacityrequired by the grid operator and equal to the maximum reactive powerlimit desired can exceed the active power maximum

For the second wind turbine, the operating conditions are such that areactive power value greater than the minimum reactive power capacityrequired by the grid operator and equal to the maximum reactive powerlimit possible cannot exceed the active power maximum.

The wind turbines with active power generation conditions that are belowthe corresponding limits of the electric drive may thereby compensate,at least in part, for the reactive power which the wind turbines with amaximum power limit desired that is below the minimum reactive powercapacity required no longer generate, thereby maximising the fraction ofthe capacity of the electric drive intended for the active powergeneration in said wind turbines, and accordingly, the active powergenerated by the wind farm. In the case of the first embodiment, thecompensation will be less, and therefore the potential to maximise theactive power generated by the wind farm will be lower than in the secondembodiment.

There is provided according to the invention a control system in whichthe control of reactive power uses reactive power generation limits foreach wind turbine which are dynamically updated according to theavailable reactive power generation capacities of each wind turbinewhich are calculated taking into account the active power operatingconditions of each of the wind turbines. The control system of the windfarm will return to each wind turbine a setpoint suitable for each ofthem, complying with the global reactive power setpoint of the farm,respecting the capacities of the electric drive of each of the windturbines and indirectly maximising the active power of the wind farm.

In certain conditions, the individual reactive power setpoints finallysent to the wind turbines will be less than the maximum reactive powerlimits desired for the first wind turbines, in which case the activepower of the farm will be maximised. As the reactive power generated bythe wind turbines with operating conditions that are such that theactive power is below the corresponding (steady, transient or dynamic)active power limits is maximised, the reactive power setpoints for thewind turbines with operating conditions that are more favorable foractive power generation will be lower.

For each one of the two previous embodiments, the control system of awind farm may also be configured to calculate an initial reactive powersetpoint for each of the wind turbines less than or equal to the firstreactive power limit. Preferably, this may be carried out in a mannerproportional to the first reactive power limit of each wind turbine andinversely proportional to the sum of the first reactive power limits ofeach of the wind turbines. Furthermore, the system is configured tocompare the global reactive power setpoint with the summation of theinitial reactive power setpoints for each wind turbine, and if thesummation of the initial reactive power setpoints for each wind turbineis less than the global Q setpoint, calculating a correction term foreach of the initial reactive power setpoints. Optionally to the latter,the system is configured to calculate a final reactive power setpointfor each wind turbine from the initial reactive power setpoint for eachwind turbine and the correction term. This calculation of the correctionterm may be performed in a proportional manner.

In particular, this calculation of the correction term for each of theinitial reactive power setpoints may be carried out in a proportionalmanner to the difference between the reactive power possible maximumlimit and the reactive power desired maximum limit of each wind turbine.

Optionally, the system is additionally configured to calculate theglobal reactive power setpoint from a voltage control.

Optionally, the system is additionally configured so that the individualsetpoints for each wind turbine do not exceed in any case their minimumreactive power capacity required.

Optionally, the system is additionally configured to receive from atleast one of the wind turbines of the wind farm a maximum reactive powerlimit possible greater than a minimum reactive power capacity required.Preferably, the at least one maximum reactive power limit possiblegreater than a minimum reactive power capacity required is dependent onan active power setpoint desired. The system is additionally configuredso that the maximum reactive power limit possible greater than a minimumreactive power capacity required does not exceed the at least onemaximum reactive power limit desired.

The invention also refers to a control method of a wind farm comprisingat least two wind turbines, wherein the method comprises the followingsteps:

-   -   calculating a global reactive power setpoint for the reactive        power to be generated by the at least two wind turbines of the        wind farm at the point of connection of the farm to the power        grid;    -   calculating individual reactive power setpoints for each of the        at least two wind turbines of the wind farm such that they add        up to the global reactive power setpoint;    -   receiving from at least one first wind turbine of one of the        wind turbines of the wind farm at least one maximum reactive        power limit desired lower than a minimum reactive power capacity        required; and    -   calculating the individual reactive power setpoints for each        wind turbine of the wind farm such that the individual reactive        power setpoint for the at least one first wind turbine is as        close as possible to the maximum reactive power limit desired.

Optionally, the at least one maximum reactive power limit desired lowerthan a minimum reactive power capacity required is dependent on aninitial active power setpoint desired.

There is also proposed a control system and a control method of a windturbine configured to calculate an initial active power setpoint basedon which a maximum reactive power limit desired is calculated and sentto the control system of a wind farm, and receiving a final reactivepower setpoint taking into account dynamic variations in the reactivepower generation possibilities of said wind turbine with respect tomaximum reactive power generation capacities. The invention also relatesto the wind turbine comprising said control system of a wind turbine.

On the other hand, the wind turbine must be configured in a suitablemanner in order to achieve the correct operation of the control methodof the wind farm:

Thus, the wind turbine is configured to calculate, based on an initialtorque (or power) control setpoint, a maximum reactive power limitdesired which would allow not limiting the initial torque (or activepower) control setpoint resulting from the control loops of the windturbine and sending it to the control system of the wind farm. Theinitial torque (or power) control setpoint corresponds to a torque (orpower) setpoint to which limitations associated with the capacities ofthe electric drive have not yet been applied; nonetheless, it can belimited based on capacities of mechanical components.

Said maximum reactive power limits desired will be taken into account,as far as possible, by the control system of the wind farm whendistributing the reactive power setpoints among the different windturbines of the wind farm required for meeting, on a global level, thereactive power generation requirements of the power grid operatorassociated for example with controls of voltage at the point ofconnection of the farm to the power grid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a general diagram of the control system and control methodof a wind farm of the present invention.

FIGS. 2A-2B show a block diagram of the control system and controlmethod of a wind farm of the present invention.

FIG. 3 shows a block diagram of the calculation of reactive powersetpoints with the system and according to the control method of a windfarm of the present invention.

FIGS. 4 and 5 show a general diagram of the control system and controlmethod of a wind turbine of the present invention.

FIG. 6 shows a comparison between a control system and control method ofa wind farm according to the state of the art and the control system andcontrol method of a wind farm according to the present invention.

PREFERRED EMBODIMENT OF THE INVENTION

The control method of a wind turbine of the present invention will bedescribed below in detail, where the wind turbine comprises:

FIG. 1 shows a general diagram of the control system and control methodof a wind farm of the present invention. Said figure shows that, basedon the operating conditions (wind speed of each Vv_1, . . . , Vv_i, typeof power curve enabled according to the mechanical limits, etc. . . . ),the wind turbines send to the control system of the wind farm SGCSinformation about reactive power generation needs (maximum reactivepower limit desired, Lim_Q_max_des) and about reactive power generationpossibilities (maximum reactive power limit possible, Lim_Q_max_pos)according to the available margin of the capacity of the electric driveand of the active power they can generate. The control system of thefarm in turn sends to them, once said maximum reactive power limitsdesired and maximum reactive power limits possible have been taken intoaccount, the individual reactive power setpoints Qref1, . . . , Qrefi tobe generated by the at least two wind turbines of the wind farm whichwill respect, as far as possible and depending on the global powersetpoint Qref_global (which can be received by the SGCS or calculated byit based on the voltage measured at the point of connection of the windfarm to the grid POI), the maximum reactive power limits desired formaximising active power production of the wind farm.

The global power setpoint Qref_global can be received by the SGCS orcalculated by it based on the voltage measured at the point ofconnection of the wind farm to the grid POI or of the power factor,according to the control that has been enabled so as to comply with thegrid integration code.

Thus, the control system of the wind farm of the invention is configuredto:

-   -   calculate a global reactive power setpoint (Qref_global) to be        generated by the at least two wind turbines of the wind farm at        the point of connection of the farm to the power grid;    -   calculate individual reactive power setpoints (Qref1, . . . ,        Qrefi) for each of the at least two wind turbines of the wind        farm such that they add up to the global reactive power setpoint        (Qref_global);    -   wherein the system is additionally configured to:    -   receive from at least one first wind turbine of the wind        turbines of the wind farm a maximum reactive power limit desired        (Lim_Q_Max_Des) lower than a minimum reactive power capacity        required of the wind turbine; and    -   calculate the individual reactive power setpoints (Qref1, . . .        , Qrefi) for each of the at least two wind turbines of the wind        farm such that the individual reactive power setpoint for the at        least one first wind turbine of the wind farm does not exceed        the maximum reactive power limit desired (Lim_Q_Max_Des).

FIGS. 2A-2B show a block diagram of the control system and controlmethod of a wind farm of the present invention. Block C includes thedetail of the system for calculating individual reactive power setpoints(reactive power individual dispatching) which would correspond to FIGS.3A-3C. The individual reactive power setpoint which is finally sent tothe wind turbines Qrefi is a setpoint corrected Q_wtg_sp3 by means ofadding the correction term Q_wtg_sp2 in FIGS. 3A-3C to a the setpointinitially calculated Qwtg_sp1, taking into account the maximum reactivepower limits possible and the maximum reactive power limits desired ofthe wind turbines. If it is possible to comply with the global setpointof the farm with this first Q setpoint, the correction term Q_wtg_sp2will have null value.

In particular, the calculation of the correction term for each of theinitial reactive power setpoints of each wind turbine may be carried outin a proportional manner to the difference between the reactive powerpossible maximum limit and the reactive power desired maximum limit ofeach wind turbine.

FIGS. 3A-3C show a block diagram of the calculation of reactive powersetpoints with the system and according to the control method of a windfarm of the present invention. In said figure there are two branches forcalculating the Q setpoints for the wind turbines, depending on whetherthe global setpoint meets an inductive Q (Q g<0) or capacitive Q (Q>0)need.

As can be seen in FIGS. 2A-2B and FIGS. 3A-3C, the control system of thewind farm of the invention is additionally configured to set at leastone first reactive power limit (Qwtg_Avail_Cap_No P_Lim,Qwtg_Avail_Ind_No P_Lim,) for each of the wind turbines chosen from themaximum reactive power limit desired and the minimum reactive powercapacity required, with the one chosen being the lowest in absolutevalue.

Since there are wind turbines with operating conditions that are suchthat they do not have the possibility of greater active power Pgeneration, and therefore they do not have a maximum reactive powerlimit desired, two implementations are possible:

-   -   all the wind turbines send the maximum reactive power limit        desired, the control system of the wind turbine setting for        those which do not have greater active power generation capacity        (Pref1<Prated) the minimum reactive power capacity required for        the wind turbine as a value for the first reactive power limit;        or    -   only those the wind turbines that do have greater active power        generation capacity (Pref1<Prated) send the maximum reactive        power limit desired, in which case the wind farm control system        sets the minimum reactive power capacity required for the wind        turbine, value which it has stored for each of the wind turbines        of the wind farm, as a value for the first reactive power limit.

FIG. 6 shows a comparison between a control system and control method ofa wind farm according to the state of the art and the control system andcontrol method of a wind farm according to the present invention.

FIGS. 4 and 5 show a general diagram of the control system and controlmethod of a wind turbine of the present invention.

Thus, the control system of the wind turbine is configured to calculate,based on an initial torque control Tref1 (or power Pref1) setpoint, amaximum reactive power limit desired (Lim_Q_Max_Des) which would allownot limiting the initial torque (or active power) control setpointresulting from the control loops of the wind turbine and sending it tothe control system of the wind farm. The initial torque (or power)control setpoint corresponds to a torque Tref1 (or power Pref1) setpointto which limitations associated with at least one maximum electriccapacity of a component of the electric drive (either of a generator orof a power converter) have not yet been applied; nonetheless, it can belimited based on the capacities of mechanical components.

This is because the generator and converter have different heatingdynamics, with the power converter generally heating up more quicklythan the generator, and therefore, they have a different capacity ofwithstanding currents greater than the rated current, capacity whichwill be dependent on the time when the current is greater than the ratedcurrent (which current can be withstood in steady-state).

In one embodiment, the step of calculating the maximum reactive powerlimit desired is performed when the operating conditions are such thatthe initial torque/active power control setpoint is greater than amaximum active power limit.

Depending on the control mode of the wind turbine (on the dynamics ofthe control loops of the wind turbine), i.e., the estimated time inwhich an above-normal active power is going to be generated (which mayentail exceeding the at least one maximum electric capacity), permanentmaximum electric capacities or transient maximum capacities both for thegenerator and for the converter will be used as a reference. In theparticular case of slow dynamics corresponding to steady control, saidmaximum active power limit corresponds with the rated active powerPrated.

If the control mode of the generator is such that an active power levelwhich could cause the rated apparent power of the generator and/orconverter to be exceeded in steady-state (i.e., a Pref1 such thatsqrt(Pref{circumflex over ( )}2+Qmax{circumflex over ( )}2)>Srated) isallowed, the permanent maximum capacities of the generator and converterare used for calculating the at least one maximum reactive power limitdesired.

The calculation will be performed as follows:Lim_Qmax_des=sqrt(Srated{circumflex over ( )}2−Pref1{circumflex over( )}2)

The control method additionally comprises the following steps:

-   -   receiving a reactive power setpoint required Qrefi from a        control system of the wind farm (SGCS)    -   calculating at least one maximum active power limit LimP2 based        on:        -   a. The at least one maximum electric capacity (it will be            either transient or permanent) in the operating conditions            of the wind turbine        -   b. The reactive power setpoint received from the control            system of the wind farm (SGCS) (Qrefi)    -   Applying at least one maximum active power limit calculated in        the step prior to the initial torque/active power control        setpoint desired for calculating a final torque/active power        control setpoint (Tref2 or Pref2).

The at least one maximum active power limit LimP2 will be calculated inone embodiment as follows:LimP2=sqrt(Sperm{circumflex over ( )}2−Qrefi{circumflex over ( )}2)

The reactive power setpoint Qrefi received from the control system ofthe wind farm (SGCS) will be sent to the control system of the powerconverter for the control of the generator.

If P_(T)ref1<Prated, it is calculated a Lim_Qmax_pos>(Qrated=windturbine minimum required capacity). On the contrary, if the operationconditions are such that P_(T)ref1<Prated, it is calculated aLim_Qmax_des<Qrated, in order to benefit from the electrical capacity togenerate power.

The invention claimed is:
 1. A control system of a wind farm comprisingat least two wind turbines, wherein the system is configured to:calculate a global reactive power setpoint for the reactive power to begenerated by the at least two wind turbines of the wind farm at thepoint of connection of the farm to the power grid; calculate individualreactive power setpoints for each of the at least two wind turbines ofthe wind farm such that they add up to the global reactive powersetpoint; receive from at least one first wind turbine of the windturbines of the wind farm a maximum reactive power limit desired lowerthan a minimum reactive power capacity required; calculate theindividual reactive power setpoints for each of the at least two windturbines of the wind farm such that the individual reactive powersetpoint for the at least one first wind turbine of the wind farm doesnot exceed the maximum reactive power limit desired; and receive fromthe at least one first wind turbine of the wind turbines of the windfarm the maximum reactive power limit desired which corresponds to thereactive power generated, wherein the reactive power which can begenerated is lower than the rated reactive power to generate an activepower greater than the rated active power.
 2. The system of claim 1,wherein the maximum reactive power limit desired lower than a minimumreactive power capacity required is dependent on an initial active powersetpoint of the at least one first wind turbine.
 3. The system of claim1, wherein the system is additionally configured to receive from atleast one second wind turbine of the wind turbines of the wind farm amaximum reactive power limit possible greater than a minimum reactivepower capacity required.
 4. The system of claim 3, wherein the maximumreactive power limit possible greater than a minimum reactive powercapacity required is dependent on an initial active power setpointdesired of the at least one second wind turbine.
 5. The system of claim3, wherein the system is additionally configured to set a first reactivepower limit for each of the wind turbines chosen from the maximumreactive power limit desired and the minimum reactive power capacityrequired, with the one chosen being the lowest in absolute value.
 6. Thesystem of claim 1, wherein the system is additionally configured to seta first reactive power limit for each of the wind turbines chosen fromthe maximum reactive power limit desired and the minimum reactive powercapacity required, with the one chosen being the lowest in absolutevalue.
 7. The system of claim 6, wherein the system is additionallyconfigured to calculate an initial reactive power setpoint for each ofthe wind turbines less than or equal to the first reactive power limit.8. The system of claim 7, wherein the system is configured to calculatethe initial reactive power setpoint for each of the wind turbines, in amanner proportional to the first reactive power limit of each windturbine and inversely proportional to the sum of the first reactivepower limits of each of the wind turbines.
 9. The system of claim 8,wherein the system is configured to compare the global reactive powersetpoint with the summation of the initial reactive power setpoints foreach wind turbine, and if the summation of the initial reactive powersetpoints for each wind turbine is less than the global Q setpoint,calculating a correction term for each of the initial reactive powersetpoints.
 10. The system of claim 8, wherein the system is configuredto calculate a final reactive power setpoint for each wind turbine fromthe initial reactive power setpoint for each wind turbine and thecorrection term.
 11. The system of claim 10, wherein the calculation ofthe correction term is performed in a proportional manner.
 12. Thesystem of claim 1, wherein the system is configured to set a firstreactive power limit for the at least one second wind turbine of each ofthe wind turbines of the wind farm equal to the maximum reactive powerlimit possible.
 13. The system of claim 12, wherein the system isadditionally configured to calculate an initial reactive power setpointfor each of the wind turbines less than or equal to the first reactivepower limit.
 14. The system of claim 1, wherein the system isadditionally configured to calculate the global reactive power setpointfrom a voltage control.
 15. The system of claim 1, wherein the system isadditionally configured so that the individual setpoints of reactivepower for each wind turbine do not exceed in any case their minimumreactive power capacity required.
 16. The system of claim 1, wherein thesystem is additionally configured to receive from at least one of thewind turbines of the wind farm at least one maximum reactive power limitpossible greater than a minimum reactive power capacity required. 17.The system of claim 16, wherein the at least one maximum reactive powerlimit possible greater than a minimum reactive power capacity requiredis dependent on an active power setpoint desired.
 18. The system ofclaim 17, wherein the system is additionally configured so that themaximum reactive power limit possible greater than a minimum reactivepower capacity required does not exceed the at least one maximumreactive power limit desired.
 19. A control method of a wind farmcomprising at least two wind turbines, wherein the method comprises thefollowing steps: calculating a global reactive power setpoint for thereactive power to be generated by the at least two wind turbines of thewind farm at the point of connection of the farm to the power grid;calculating individual reactive power setpoints for each of the at leasttwo wind turbines of the wind farm such that they add up to the globalreactive power setpoint; receiving from at least one first wind turbineof one of the wind turbines of the wind farm at least one maximumreactive power limit desired lower than a minimum reactive powercapacity required; calculating the individual reactive power setpointsfor each wind turbine of the wind farm such that the individual reactivepower setpoint for the at least one first wind turbine is as close aspossible to the maximum reactive power limit desired; wherein in thestep of receiving from at least one first wind turbine of the windturbines of the wind farm at least one maximum reactive power limitdesired, the at least one maximum reactive power limit desiredcorresponds to the reactive power which can be generated, wherein thereactive power which can be generated is lower than the rated reactivepower to generate an active power greater than the rated active power.20. The method of claim 19 wherein the at least one maximum reactivepower limit desired lower than a minimum reactive power capacityrequired is dependent on an initial active power setpoint desired.
 21. Acontrol system of a wind farm comprising at least two wind turbines,wherein the system is configured to: calculate a global reactive powersetpoint for the reactive power to be generated by the at least two windturbines of the wind farm at the point of connection of the farm to thepower grid; calculate individual reactive power setpoints for each ofthe at least two wind turbines of the wind farm such that they add up tothe global reactive power setpoint; receive from at least one first windturbine of the wind turbines of the wind farm a maximum reactive powerlimit desired lower than a minimum reactive power capacity required;calculate the individual reactive power setpoints for each of the atleast two wind turbines of the wind farm such that the individualreactive power setpoint for the at least one first wind turbine of thewind farm does not exceed the maximum reactive power limit desired; andreceive from the at least one first wind turbine of the wind turbines ofthe wind farm the maximum reactive power limit desired which correspondsto the reactive power which can be generated, wherein the reactive powerwhich can be generated is lower than the rated reactive power so thatthe steady active power exceeds the rated active power.
 22. A controlsystem of a wind farm comprising at least two wind turbines, wherein thesystem is configured to: calculate a global reactive power setpoint forthe reactive power to be generated by the at least two wind turbines ofthe wind farm at the point of connection of the farm to the power grid;calculate individual reactive power setpoints for each of the at leasttwo wind turbines of the wind farm such that they add up to the globalreactive power setpoint; receive from at least one first wind turbine ofthe wind turbines of the wind farm a maximum reactive power limitdesired lower than a minimum reactive power capacity required; calculatethe individual reactive power setpoints for each of the at least twowind turbines of the wind farm such that the individual reactive powersetpoint for the at least one first wind turbine of the wind farm doesnot exceed the maximum reactive power limit desired; and receive fromthe at least one first wind turbine of the wind turbines of the windfarm the maximum reactive power limit desired which corresponds to thereactive power which can be generated, wherein the reactive power whichcan be generated is lower than the rated reactive power thus generatingan active power greater than the rated active power without exceedingthe limit set by the apparent power.
 23. A control system of a wind farmcomprising at least two wind turbines, wherein the system is configuredto: calculate a global reactive power setpoint for the reactive power tobe generated by the at least two wind turbines of the wind farm at thepoint of connection of the farm to the power grid; calculate individualreactive power setpoints for each of the at least two wind turbines ofthe wind farm such that they add up to the global reactive powersetpoint; receive from at least one first wind turbine of the windturbines of the wind farm a maximum reactive power limit desired lowerthan a minimum reactive power capacity required; calculate theindividual reactive power setpoints for each of the at least two windturbines of the wind farm such that the individual reactive powersetpoint for the at least one first wind turbine of the wind farm doesnot exceed the maximum reactive power limit desired; and receive fromthe at least one first wind turbine of the wind turbines of the windfarm the maximum reactive power limit desired which corresponds to thereactive power which can be generated, wherein the reactive power whichcan be generated is lower than the rated reactive power thus generatingan active power greater than the rated active power based on a finalreactive power setpoint calculated for each of the at least two windturbines of the wind farm.